I'm having minor issues with the FindMinimum function when using NIntegrate inside. The functions work perfectly well but I get warning messages and I was wondering if maybe I could be enlightened on the correct usage of these two functions together.

For the sake of illustration I provide the full set of functions I used on a simple example.

NIntegrate::inumr: "The integrand (a.{(8 Piecewise[{<<2>>},0])/\[Pi]^3+(8 Piecewise[{<<2>>},0])/\[Pi]^3}+b.{1/2\\[Pi]\(8\Power[<<2>>]\Piecewise[<<2>>]+8\Power[<<2>>]\Piecewise[<<2>>])}-1/2\\[Pi]\((8 Piecewise[{{<<2>>},{<<2>>}},0])/\[Pi]^3+(8 Piecewise[{{<<2>>},{<<2>>}},0])/\[Pi]^3)+1/2\\[Pi]\((8 Piecewise[{{<<2>>},{<<2>>}},0])/\[Pi]^3+(8 Piecewise[{{<<2>>},{<<2>>}},0])/\[Pi]^3))^2 has evaluated to non-numerical values for all sampling points in the region with boundaries {{0,3.14159}}"

I ask about this because FindMinimum takes unexpectedly long time to converge to the solution (which is a right one). But I thought that maybe using the functions correctly will accelerate the process.

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